Have you ever seen a duck's penis?

Long duck penis is looooooooooooooooooooong. Look:

(Somewhat NSFW, it's a video of a duck's penis)

Before its emergence, a drake’s penis is usually completely hidden from view, tucked inside his body like an inside-out sock. Drakes unfurl their pensises differently than male mammals. In mammals, the penis becomes erect as blood flows into the spongy tissue. Ducks pump lymph fluid instead. And as the fluid enters the penis, it does not simply become engorged. It flips rightside-out.

Link | via